\begin{table}%t1
%\centering
\par
\caption{The UHECR ($>$$10^{10}$~GeV) fraction generated by relativistic Fermi acceleration in the Monte-Carlo simulation. A number of 50 layers is considered here and the flow duration varies from 0.5~s (short~GRB) to 10.0~s (long~GRB). The magnetic field decreases as~$r^{-3/2}$.\label{restab}    }    
\begin{tabular}{cccc}      
\hline\hline     
Flow duration (in s)     
& \multicolumn{3}{c}{Magnetic field at $r_{\rm b}$}\\     
& $10^{4}$~G & $10^{5}$~G & $10^{6}$~G \\      
\hline     
0.5 & $5.4\times 10^{-5}$ & $1.5\times 10^{-4}$  & $3.6\times 10^{-4}$ \\     
\hline     
1.0 & $6.3\times 10^{-5}$ & $1.9\times 10^{-4}$ & $4.1\times 10^{-4}$\\     
\hline     
5.0 & $5.1\times 10^{-5}$ & $1.8\times 10^{-4}$ & $4.8\times 10^{-4}$\\     
\hline     
10.0 & $2.0\times 10^{-5}$ & $1.2\times 10^{-4}$ & $3.2\times 10^{-4}$\\     
\hline     
\end{tabular}     
\end{table}